Solar thermochemical reactor, methods of manufacture and use thereof and thermogravimeter

ABSTRACT

A solar thermochemical reactor contains an outer member, an inner member disposed within an outer member, wherein the outer member surrounds the inner member and wherein the outer member has an aperture for receiving solar radiation. An inner cavity and an outer cavity are formed by the inner member and outer member and a reactive material that is capable of being magnetically stabilized is disposed in the outer cavity between the inner member and the outer member.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of International Application No.PCT/US12/71332, filed on Dec. 21, 2012, which claims the benefit of U.S.Application No. 61/579,449, filed on Dec. 22, 2011, which isincorporated herein by reference in their entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR SUPPORT

The United States Government may have rights in this invention pursuantto grant proposals having Funding Opportunity Nos. DE-FOA-0000103 andDE-FOA-0000471 to the U.S. Department of Energy/Advanced ResearchProjects Agency—Energy (ARPA-E).

BACKGROUND

This disclosure relates to a solar thermochemical reactor, methods ofmanufacture, and uses thereof and a thermogravimeter.

Solar thermochemistry is a newly emerging technology for the productionof fuels using highly concentrated solar radiation. Solar power is usedto facilitate thermochemical reactions. Solar thermochemical reactorsare in the early stages of development. Significant challenges are posedby the use of solar energy as a renewable energy source, which makes itdifficult to deploy on a large scale. Solar energy is, by its nature,transient as it is dependent upon exposure to the sun. Solarthermochemical reactions can proceed at very high temperatures. Solarchemical reactors can also employ a window manufactured from anoptically transparent material (e.g., glass, plastic, or combinationsthereof) to admit highly concentrated radiation to the reaction site.The optically transparent material can be structurally weak andextremely susceptible to staining and subsequent damage due to thermalstresses. In addition, thermochemical reactions can result in sinteringof the reactant materials that reduces their internal surface area andadversely affects the chemical kinetics of the reaction.

It is therefore desirable to develop solar thermochemical reactors whichoperate under lower temperature conditions, do not use a window that ismanufactured from an optically transparent material and facilitatecontrol of the chemical kinetics of the thermochemical reaction. It isalso desirable to develop a method of using solar thermochemicalreactors in a manner which maximizes the availability of solar energyduring non-transient periods.

SUMMARY

Disclosed herein is a solar thermochemical reactor comprising an outermember, an inner member disposed within and surrounded by the outermember, wherein the outer member has an aperture for receiving solarradiation, an inner cavity and an outer cavity formed by the inner andouter members, respectively, and a reactive material capable of beingmagnetically stabilized wherein the reactive material is disposed in theouter cavity between the inner member and the outer member.

Disclosed herein too is a method of making a solar thermochemicalreactor comprising disposing an inner member within an outer member thatsurrounds the inner member wherein the outer member has an aperture forreceiving solar radiation and disposing a reactive material capable ofbeing magnetically stabilized between the inner member and the outermember.

Disclosed herein too is a method of using a solar thermochemical reactorcomprising disposing an inner member within an outer member, wherein theouter member surrounds the inner member, disposing a reactive materialcapable of being magnetically stabilized in between the outer member andthe inner member, applying a vacuum to the outer member, fluidizing thereactive material, applying a magnetic field at least partially aroundthe outer member; disposing solar radiation onto the outer member,carrying out a reduction reaction in the reactor, extracting oxygen fromthe outer member; disposing carbon dioxide and water onto the reactormaterial, carrying out an oxidation reaction in the reactor andextracting carbon monoxide gas and hydrogen gas from the outer member.

Disclosed herein too is a cycling loop process for producing syntheticgas comprising disposing a first solar thermochemical reactor in closeproximity to a second solar thermochemical reactor, focusing solarradiation from a concentrated source onto the first solar thermochemicalreactor, carrying out a reduction reaction in the first solarthermochemical reactor, focusing solar radiation from the concentratedsource onto a second solar thermochemical reactor, and carrying out areduction reaction in the second solar thermochemical reactor whereinthe first reactor and second reactor each comprise an outer memberhaving an aperture for receiving solar radiation, wherein said outermember completely surrounds an inner member, wherein the outer memberand inner member form an inner cavity and outer cavity and furtherwherein a reactor material capable of becoming magnetically stabilizedis disposed in the outer cavity.

Disclosed herein too is a solar thermogravimeter for modeling thekinetics of thermochemical reactions in a solar thermochemical reactorcomprising a metal pressure vessel, a tubular or dome shaped quartzvessel for optical access, a low vibration vacuum pump, an analyticalbalance disposed within the low pressure vessel, a temperature sensor, athermocouple, a flow meter and a gas phase chromatograph or massspectrometer.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1A is a depiction of an exemplary solar thermochemical reactor;

FIG. 1B is a depiction of another exemplary solar thermochemicalreactor;

FIG. 2A is a depiction of a cross section of an exemplary solarthermochemical reactor in which a reduction reaction occurs;

FIG. 2B is a depiction of a cross section of an exemplary solarthermochemical reactor in which an oxidation reaction occurs;

FIG. 3 is a depiction of an exemplary cyclic looping process using twosolar thermochemical reactors in close proximity to one another;

FIG. 4 is a depiction of an exemplary reactor setup;

FIG. 5A is a depiction of an exemplary thermogravimeter using atubular-shaped reactor;

FIG. 5B is a depiction of an exemplary thermogravimeter using adome-shaped reactor;

FIG. 6 is a graph showing the disassociation temperature, reactionenthalpy, and losses due to pump work as a function of absolute pressurefor the iron oxide reactor material matrix, specifically, thedisassociation temperature as a function of pressure for the purelythermal reduction reaction temperature for which the Gibbs free energychange of reaction equals zero;

FIG. 7 show the output from a thermogravimetric analysis (TGA)demonstrating the cyclic reactivity for three redox cycles;

FIG. 8 is a graph showing thermogravimetric analysis (TGA) results forthe oxidation of activated carbon during a temperature ramp to 1000° C.at 5° C./min; and

FIG. 9 shows photomicrograph (at two different magnifications) of themonolithic solid after the activation of carbon is completed.

DETAILED DESCRIPTION

It will be understood that when an element is referred to as being “on”another element, it can be directly on the other element or interveningelements may be present therebetween. In contrast, when an element isreferred to as being “directly on” another element, there are nointervening elements present. As used herein, the term “and/or” includesany and all combinations of one or more of the associated listed items.

It will be understood that, although the terms first, second, third,etc. may be used herein to describe various elements, components,regions, layers and/or sections, these elements, components, regions,layers and/or sections should not be limited by these terms. These termsare only used to distinguish one element, component, region, layer orsection from another element, component, region, layer or section. Thus,a first element, component, region, layer or section discussed belowcould be termed a second element, component, region, layer or sectionwithout departing from the teachings of the present invention.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting. As used herein, thesingular forms “a,” “an” and “the” are intended to include the pluralforms as well, unless the context clearly indicates otherwise. It willbe further understood that the terms “comprises” and/or “comprising,” or“includes” and/or “including” when used in this specification, specifythe presence of stated features, regions, integers, steps, operations,elements, and/or components, but do not preclude the presence oraddition of one or more other features, regions, integers, steps,operations, elements, components, and/or groups thereof.

Furthermore, relative terms, such as “lower” or “bottom,” “upper” or“top,” and “inner” or “outer” may be used herein to describe oneelement's relationship to another element as illustrated in the Figures.It will be understood that relative terms are intended to encompassdifferent orientations of the device in addition to the orientationdepicted in the figures. For example, if the device in one of thefigures is turned over, elements described as being on the “lower” sideof other elements would then be oriented on “upper” sides of the otherelements. The exemplary term “lower,” can therefore, encompass both anorientation of “lower” and “upper,” depending on the particularorientation of the figure. Similarly, if the device in one of thefigures is turned over, elements described as “below” or “beneath” otherelements would then be oriented “above” the other elements. Theexemplary terms “below” or “beneath” can, therefore, encompass both anorientation of above and below.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this invention belongs. It will befurther understood that terms, such as those defined in commonly useddictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art and thepresent disclosure, and will not be interpreted in an idealized oroverly formal sense unless expressly so defined herein.

Exemplary embodiments are described herein with reference to crosssection illustrations that are schematic illustrations of idealizedembodiments. As such, variations from the shapes of the illustrations asa result, for example, of manufacturing techniques and/or tolerances,are to be expected. Thus, embodiments described herein should not beconstrued as limited to the particular shapes of regions as illustratedherein but are to include deviations in shapes that result, for example,from manufacturing. For example, a region illustrated or described asflat may, typically, have rough and/or nonlinear features. Moreover,sharp angles that are illustrated may be rounded. Thus, the regionsillustrated in the figures are schematic in nature and their shapes arenot intended to illustrate the precise shape of a region and are notintended to limit the scope of the present claims.

The transition term “comprising” encompasses the transition terms“consisting of” and “consisting essentially of.”

Various numerical ranges are disclosed herein. These ranges areinclusive of the endpoints as well as numerical values between theseendpoints. The numbers in these ranges and those on the endpoints areinterchangeable.

Solar energy is the most abundant source of renewable energy. Becausesolar energy is an intermittent power source, storage of this energy isdesirable for large-scale deployment and production of fuels. Solarthermochemistry can be used to produce synthetic gas (“syngas”), aprecursor used for the production of clean and carbon neutral synthetichydrocarbon fuels such as methanol, methane or synthetic petroleum.Solar thermochemistry can also be used to store concentrated solarenergy in chemical energy carriers until production of syngas or fuel isdesired. Thermochemical storage of concentrated solar energy isdesirable because chemical energy carriers have a high energy density,are stable, can be stored indefinitely; and a complete infrastructurefor their transport and storage already exists, i.e., the existinginfrastructure for hydrocarbon fuel transport and storage.

Solar thermochemical reactors can have windowed in which the window ismanufactured from an optically transparent material. Such windoweddesigns present reliability issues due to weakness in mechanicalstructure and staining and limit the size of reactors, making itdifficult to scale up solar reactor technology to an industrial level.In addition, metal reactor materials used in solar thermochemicalreactors can be subject to undesirable sintering, which reduces thesurface area of the metal reactor materials and causes the period duringwhich the metal reactor materials are used for repeated reactor reactioncycles to become significantly reduced. The thermochemical reactionswhich are carried out in solar reactors also involve significant periodsof time. For example, a single cycle to produce syngas using reductionand oxidation can take up to five hours.

Two-step metal oxide looping processes involve a reduction reaction andan oxidation reaction to complete one “redox” cycle. The directthermolysis of water can involve temperatures in excess of 2500° C.Two-step metal oxide looping processes can be advantageous because theyavoid these extreme temperatures. Two-step metal oxide looping processesusing volatile metal oxides such as zinc oxide can have disadvantagesassociated with avoiding recombination of the highly reactive gaseousmetal-oxygen mixture produced. Such processes can also involve hightemperatures to carry out the solar reduction/metal disassociation step.

Disclosed herein are reactors, methods of manufacture and use thereofand thermogravimeters which address one or more of the above-describedchallenges. Disclosed herein is a solar thermochemical reactorcomprising an outer member, an inner member disposed within andsurrounded by the outer member, wherein the outer member has an aperturefor receiving solar radiation, an inner cavity and an outer cavityformed by the inner and outer members, respectively and a reactivematerial capable of being magnetically stabilized wherein the reactivematerial is disposed in the outer cavity between the inner member andthe outer member.

Disclosed herein too is a method of making a solar thermochemicalreactor comprising disposing an inner member disposed within an outermember that surrounds the inner member wherein the outer member has anaperture for receiving solar radiation and disposing a reactive materialcapable of being magnetically stabilized between the inner member andthe outer member.

In an exemplary embodiment, as depicted in FIG. 1A, the solarthermochemical reactor 10 comprises an outer member 20, an inner member30 disposed within the outer member 20 wherein the outer member 20completely surrounds the sides, top and bottom of the inner member 30,and further wherein the outer member 20 has an aperture 40 for receivingsolar radiation. An inner cavity 50 is formed inside the inner member 30and an outer cavity 60 is formed in between the inner member 30 and theouter member 20. The inner cavity 20 allows solar radiation in, and theradiation is trapped within the cavity and eventually absorbed by thecavity walls. A reactive material 70 capable of being magneticallystabilized is disposed in the outer cavity 60. The outer member 20further comprises a material port 80 from which reaction products areextracted and reactant materials may be introduced. The inner and outermembers 20, 30 of the reactor are of any shape known to those of skillin the art, specifically a cylindrical shape. In an exemplaryembodiment, the reactor 10 comprises a single inner member 30, a singleouter member 20, a single inner cavity 50 and a single outer cavity 60.

The use of an aperture 40 with the dual cavity design overcomes thestructural weakness and efficiency problems associated with the use ofoptically transparent materials (e.g., glass, plastic, or combinationsthereof) in windows in reactor systems. Accordingly, the reactor 10 hasan aperture 40 which is devoid of an optically transparent material. Inan embodiment, the aperture 40 comprises a media that has a refractiveindex of about 1.0 to about 1.05. In another embodiment, the aperture 40comprises a media that has a density of about 0.90 to about 1.50 kg/m³.In yet another embodiment, the aperture 40 comprises a fluid. In anexemplary embodiment, the aperture 40 comprises a fluid wherein thefluid is air.

In another exemplary embodiment, as depicted in FIG. 1B, the outermember 20 of the reactor assembly 10 further comprises a front plate 90which is detachable from a first end of the outer member 20 whichsurrounds the inner member 30. The outer member 20 also furthercomprises a rear plate 100 is detachable from a second end of the outermember 20. The second end is opposed to the first end. The front plate90 and/or rear plate 100 are used to facilitate the loading of reactivematerials (capable of becoming magnetically stabilized) into the outercavity 60 and unloading of spent reactive materials from the outercavity 60. The front plate 90 and/or rear plate 100 are formed to fitover the inner member 30 and outer member 20, thereby also covering theinner cavity 50 and the outer cavity 60. The front plate 90 and rearplate 100 comprise grooved seals 110 that form a self-aiding fit overthe ends of the inner member 30 and outer member 20. In an embodiment,the outer member 20 is used in conjunction with a vacuum pump to tightlyseal the assembled parts of the reactor. The reactor 10 has a vacuumline running from the outer member 20 of the reactor to a vacuum pump(not shown). The vacuum pump is in fluid communication with the reactor10. Alternatively, in another embodiment, the outer member 20 is formedsuch that it completely surrounds the inner member 30 without having afront plate 90 and/or rear plate 100. In other words, the outer member20 and the inner member 30 are formed in a single piece with ports tointroduce and remove materials from them.

In an embodiment, the outer member 20 further comprises a shutter whichexposes or covers the aperture 40 in the outer member 20 for receivingsolar radiation as desired. The shutter 120 can be seen in the FIGS. 2Aand 2B. The shutter 120 is optionally attached to the reactor 10. In oneembodiment, the shutter 120 has its own support and activation mechanism(not shown). When the shutter 120 is open, solar radiation is permittedto enter into the reactor 10, thereby producing heat. When the shutter120 is closed, solar radiation is prevented from entering the reactor10, and the heat inside the reactor is conserved while re-radiation isprevented. The use of the shutter 120 in open and closed modes promotesthe efficiency of the thermochemical reactions carried out in thereactor 10. No external heating is used to carry out the thermochemicalreactions in the reactor 10. In an embodiment, the solar radiation whichthe aperture 40 receives is in the form of concentrated radiation.

Referring back to FIGS. 1A and 1B, the inner member 30, outer member 20,face plate 90 and rear plate 100 are made of any material which iscapable of withstanding the temperatures used to carry outthermochemical reactions in the reactor 10. Exemplary materials includerefractory materials, specifically ceramics, more specifically zirconia,silicon carbide, zinc and alumina oxides or mixtures thereof. In anembodiment, the front plate 90 and rear plate 100 comprises groovedseals, specifically, metal enforced grooved seals, and more specificallygraphite metal enforced seals, to fit over the ends of the inner member30 and the outer member 20.

The dual cavity design of the reactor 10 maximizes the effectiveabsorbance of solar radiation in the reactor 10 and minimizesre-radiation losses. The use of a vacuum reduces the temperatures usedto carry out thermochemical reduction reactions in the solarthermochemical reactor 10.

In another exemplary embodiment, as depicted in a cross section of thereactor assembly shown in FIG. 2A, the outer member 20 of the reactor 10further comprises an insulating material 130. The insulating material130 is internal or external to the outer member 20. The outer member 20also comprises a magnetic coil 140. In an embodiment, the magnetic coil140 is affixed or disposed externally to or within at least part of theouter member 20 or disposed externally to the outer member 20. Inanother embodiment, the magnetic coil 140 is physically separate fromthe outer member 20 and placed in a position external and adjacent tothe outer member 20. Affixing or disposing the insulation material andmagnetic coil so as to form part of the outer member 20 of the reactorassembly 10 is desirable for commercial packaging and efficiency of use.The magnetic coil 140 is used to apply a magnetic field to the outermember 20 and thereby magnetically stabilizes the reactor materials 70inside the outer cavity 60 of the reactor assembly 10.

The reactor material 70 comprises particles which are capable ofbecoming magnetically stabilized. Exemplary materials are described indetail in U.S. Provisional Patent Application No. 61/505,890 filed onJul. 8, 2011, which is incorporated by reference in its entirety herein.Specifically, exemplary reactor materials 70 include metal oxides suchas iron, iron oxides or mixtures thereof. More specifically, exemplaryreactor materials 70 are selected from the group consisting of Fe₂O₃,Fe₃O₄, and NiFe₂O₄ or a combination including at least one of theforegoing. In an embodiment, the metal oxide reactor materials 70 arenon-volatile. Another group of exemplary reactor materials 70 arecarbonaceous materials. An example of such carbonaceous materials areactivated carbon. Activated carbon is also called activated charcoal oractivated coal and is a form of carbon that is riddled with small,low-volume pores that increase the surface area available for adsorptionor chemical reactions. The activated carbon is mixed into ferrite powderand oxidized using either air or steam to form the reactor material 70.During the oxidation, the activated carbon is converted from a solid toa gas, i.e., from carbon to carbon dioxide. Since the activated carbonis all converted to carbon dioxide during the oxidation, the resultingreactor material contains only the oxidized porous ferrite powder.Non-volatile metal oxides, when used solar thermochemical reactions,avoid undesirable properties associated with volatile metal oxidesassociated with rapid quenching.

The reactor materials 70 form a bed of reactor materials within theouter cavity 60. The bed of reactor materials is then fluidized. When amagnetic field is applied to the outer member 20, and solar radiation isdisposed upon the aperture 40, the temperature is elevated, and the bedof reactor materials 70 becomes magnetically stabilized. Iron powdersinters at 550° C. when oxidized. Therefore, the magnetically stabilizedbed is sintered at a relatively low temperature. This results insintering of the reactor materials 70 into a state in which the surfacearea is not substantially reduced. The exposure to a magnetic field hasthe effect of freezing the reactor materials 70 into a structure with ahigh surface area. The particle chains within the reactor materials 70repel each other due to the magnetic force, creating a high surface areastructure with high porosity which can withstand exposure to relativelyhigh temperatures during the first reduction reaction of the redoxcycle. In an embodiment, the magnetic field is only used duringsynthesis of the magnetically stabilized bed structure prior to thefirst reduction reaction carried out in the solar reactor using thereactor materials 70. The magnetically stabilized bed of reactormaterials can overcome the sintering problems associated with otherreactive materials which become sintered such that the surface area isreduced, and therefore undergo favorable chemical kinetics duringreactor cycles. Accordingly, the reactor materials 70 disclosed hereinavoid deactivation due to undesirable sintering and are capable of beingused for many repeated reaction cycles in the reactor 10 withoutrequiring new reactor materials to be loaded into the reactor.

The dual cavity design of the reactor 10 and magnetically stabilizedreactor materials 70 used therein are used at relatively low pressures,thereby overcoming the challenges of other reactor systems which usehigh temperatures and high pressures. The reaction temperatures in thereduction reaction are lowered by lowering the partial pressure of theoxygen evolving as a result of the reaction. The low pressure utilizedalso allows for lower temperature conditions for carrying out thereduction reaction in the reactor 10. In an exemplary embodiment, thedual cavity solar thermochemical reactor 10 is operated at partialoxygen pressures of less than about 10⁻⁴ bar, specifically less than10⁻³ bar, and more specifically less than 5×10⁻⁴ bar to facilitate thedisassociation of the metal in the reactor material 70. In anotherexemplary embodiment, the dual cavity solar thermochemical reactor maybe operated at temperatures of less than 1500° C., specifically lessthan 1500° C., and more specifically less than 1450° C. In anotherembodiment, the dual cavity design of the reactor 10 has a low thermalmass and is equipped with a control system to control irradiation inorder to cope with transient periods of availability of solar radiation.In addition, waste heat from the reactor discharge gases are recouped,and transferred to the inlet reactants, H₂O and CO₂, to increase energyconversion efficiency.

Fracturing, caused by matrix mismatch or spallation of the metal oxidereactor material 70 is controlled by controlling the growth conditions,specifically the film thickness and/or rate of growth. In anotherembodiment, short duration redox cycles are used to avoid spallation andfracture. In yet another embodiment, use of a magnetically stabilizedfluidized bed of reactor materials 70 avoids fracturing and spallation.

Disclosed herein too is a method of using a solar thermochemical reactorcomprising disposing an inner member within an outer member, wherein theouter member surrounds the inner member, disposing a reactive materialcapable of being magnetically stabilized in between the outer member andthe inner member, applying a vacuum to the outer member, fluidizing thereactive material, applying a magnetic field at least partially aroundthe outer member; disposing solar radiation onto the outer member,carrying out a reduction reaction in the reactor, extracting oxygen fromthe outer member; disposing carbon dioxide and water onto the reactormaterial, carrying out an oxidation reaction in the reactor andextracting carbon monoxide gas and hydrogen gas from the outer member.

As depicted in FIGS. 2A and 2B, the reactor 10 is used to performthermochemical redox reactions. A complete solar thermochemical reactorredox cycle comprises a reduction reaction and an oxidation reaction toproduce syngas. The resulting syngas is then stored or further refinedinto fuels for commercial use. As depicted in FIG. 2A, in reductionmode, the reactor 10 uses concentrated solar radiation to produce heatand elevate the temperature of the reactor 10. The reactive material 70undergoes reduction at low pressure to produce oxygen (O₂), which isextracted from the reactor via the material port 80. During thereduction step, the reactor material 70, or metal oxide, undergoesdisassociation wherein metal is dissociated from the metal oxide.Specifically, exemplary reduction reactions are represented by thefollowing chemical equations:Fe₃O₄+solar heat→3FeO+0.5O₂Fe2O₃+solar heat→2FeO+0.5O₂NiFe₂O₄+solar heat→NiFe₂O₃+0.5O₂In an embodiment, the reduction of reactive materials 70 in the solarthermochemical reactor 10 results in reduction to iron, although this isless probable than the equations represented above, and is representedby the following exemplary chemical equation:Fe₃O₄+solar heat→3Fe+2O₂

In an exemplary embodiment, as depicted in FIGS. 1A and 2A, reactivematerial 70 is disposed in the outer cavity 60 of the reactor 10. Avacuum is applied to the reactor assembly 10 creating a fitted sealbetween the outer member 20, the inner member 30, the front plate 90 andrear plate 100, aided by the grooved seals 110. The reactive material 70is then fluidized. A magnetic field is applied to the bed of reactivematerial 70 via the magnetic coil 140, magnetically stabilizing thereactive material 70. The shutter 120 is opened, allowing concentratedsolar radiation to be received into the reactor through the aperture 40.The magnetic field is then turned off. The concentrated radiationproduces heat, elevating the temperature in the reactor 10 to sinter thereactor materials 70 and to drive the reduction reaction. Themagnetically stabilized, sintered reactive material 70 undergoesreduction to produce oxygen gas, which is extracted from the reactor viathe material port 80.

After the thermochemical reduction reaction is complete, the shutter 120is closed, preventing solar radiation from entering the aperture 40 ofthe outer member 20. The reactor 10 is then used to carry out athermochemical oxidation reaction in oxidation mode. The closed shutter120 allows heat generated in the reactor to be retained and helps tominimize radiation loss.

In an exemplary embodiment, as depicted in FIG. 2B, in oxidation mode,water (H₂O) and carbon dioxide (CO₂) are introduced into the reactor 10via the material port 80 to oxidize the magnetically stabilized bed ofreactive material 70. The reactive material 70 undergoes oxidation atatmospheric pressure to produce carbon monoxide and hydrogen gases, orsyngas, which is extracted from the reactor via the material port 80.The heat produced from the exothermic oxidation reaction is sufficientto maintain the temperature. Specifically, exemplary oxidation reactionsare represented by the following chemical equations:3FeO+H₂O+CO₂→Fe₃O₄+H₂+CO2FeO+H₂O+CO₂→Fe₂O₃+H₂+CO3Fe+4H₂O+CO₂→Fe₃O₄+4H₂+CO2NiFe₂O₃+H₂O+CO₂→2NiFe₂O₄+H₂+CO

The thermochemical reduction reaction and oxidation reaction togetherconstitute a single redox cycle. The resulting syngas is refined intofuel for commercial use or stored for later refinement. In anembodiment, the magnetically stabilized bed material is used for manycycles, specifically many hundred cycles, and more specificallythousands of cycles, before being replaced. In another embodiment, theredox reactions are carried out in short duration cycles. For example, acomplete redox cycle is carried out in about one hour, more specificallyin about 15 minutes.

In yet another exemplary embodiment, a looping process is provided asdepicted in FIG. 3. As shown in FIG. 3, a first solar thermochemicalreactor 10 is disposed in close proximity to a second solarthermochemical reactor 15. Concentrated radiation, such as that from anadjustable heliostat field 25, is focused onto the first reactor 10wherein the shutter is open. A reduction reaction as described above iscarried out and once completed, the shutter is closed, allowing theoxidation reaction to produce syngas to proceed. Once the reductionreaction in the first reactor 10 is completed, and while the oxidationreaction is being carried out in the first reactor 10, the concentratedsolar radiation is refocused onto the second reactor 15, which similarlyundergoes a reduction reaction. Once the reduction reaction in thesecond reactor 15 is completed, the concentrated solar radiation isagain refocused from the heliostat 25 onto the first reactor 10, and thelooping process begins again. The looping process maximizes efficiencyby increasing the use of available solar radiation during the redoxcycle. This looping process uses two or more reactors located in closeproximity to each other. The looping process is repeated over and over,thus minimizing downtime during periods when solar radiation isavailable between redox cycles. The looping process and reactor systemhave a solar-to-chemical fuel conversion efficiency of about 10%,specifically about 25% or greater based on a 1MW scale reactor design.The looping process overcomes the challenges associated with thecyclical and transient nature of solar thermochemical reactor operation.

Two or more reactors in close proximity to one another are used in thelooping process. In one embodiment, at least two reactors are disposedside-by-side. In another embodiment, at least one reactor is disposed ontop of at least one other reactor. In another embodiment, the shiftingof the solar radiation onto to reactor is accomplished by shifting aheliostat to move the concentrated solar radiation from one reactor toanother. In another embodiment, two or more reactors are disposed upon arotating reactor assembly which refocuses concentrated solar radiationfrom one reactor to another. In yet another embodiment, abeam-redirected mirror is used to refocus concentrated solar radiationfrom one reactor to another.

In an exemplary embodiment, a solar reactor having a dual cavity designas described above has an aperture 40 that does not include an opticallytransparent material, operates at a relatively a low pressure andtemperature to carry out the metal dissociation reduction step, andmagnetically stabilized reactor materials are sintered in a controlledmanner to avoid undesirable sintering and deactivation of the metalreactor materials.

In another embodiment, as depicted in FIG. 4, a reactor system 150 isequipped with means to automatically carry out the redox cycles. Thereactor system 150 comprises a first solar thermochemical reactor 10disposed in close proximity and in fluid communication with a secondsolar thermochemical reactor 15. A steam generator 160 is disposedupstream from and in fluid communication with the first solarthermochemical reactor 10 and the second solar thermochemical reactor15. A first controller 170 is disposed upstream of the steam generator160 from which water is supplied. The first controller 170 controls theflow rate of water supplied to the steam generator 160. In anembodiment, the flow rate of the water entering the steam generator 160is from about 0.1 g-cm² to about 1.0 g-cm². The steam generator 160elevates the temperature of the water supplied by the first controller170 to generate steam. The temperature in the steam generator 160 whichis used to convert water to steam is from about 200° C. to about 500° C.The steam is then supplied from the steam generator 160 to the firstsolar thermochemical reactor 10 and the second solar thermochemicalreactor 15 for use in the redox cycle reactions carried out therein.

The reactor system 150 further comprises a heat exchanger 180 disposedupstream from and in fluid communication with the first solarthermochemical reactor 10 and the second solar thermochemical reactor15. A second controller 190 is disposed upstream of the heat exchanger180 from which carbon dioxide is supplied. The second controller 190controls the flow rate of carbon dioxide supplied to the heat exchanger180. In an embodiment, the flow rate of the carbon dioxide entering theheat exchanger 180 is from about 0.1 g-cm² to about 1.0 g-cm². The heatexchanger 180 elevates the temperature of the carbon dioxide suppliedfrom second controller 190. The temperature in the heat exchanger 180which is used to elevate the temperature of the carbon dioxide is fromabout 25° C. to about 400° C. The carbon dioxide is then supplied fromthe heat exchanger 180 to the first solar thermochemical reactor 10 andthe second solar thermochemical reactor 15 for use in the redox cyclereactions carried out therein.

The reactor system 150 further comprises means for heat recuperation. Afirst vacuum pump 192 and a second vacuum pump 194 are disposeddownstream of and in fluid communication with the first solarthermochemical reactor 10 and the second solar thermochemical reactor15. The first vacuum pump 192 and second vacuum pump 194 remove oxygenproduced from the redox cycle reactions which occur in the reactors.Heat generated from the redox cycle reactions carried out in the firstsolar thermochemical reactor 10 and the second solar thermochemicalreactor 15, and the hydrogen and carbon monoxide reaction products, aresupplied to the steam generator 160 where the heat is used to generatesteam from water. The heat is supplied from the steam generator 160 tothe heat exchanger 180 where the heat is used to elevate the temperatureof the carbon dioxide reaction product and the reaction products arecollected. In another embodiment, the reactor system 150 also includesother heat recuperation technology.

Disclosed herein too is a solar thermogravimeter for modeling thekinetics of thermochemical reactions in a solar thermochemical reactor.The thermogravimeter facilitates modeling of thermochemical reactions tooptimize reaction conditions and increase efficiency of operations in asolar reactor.

In an exemplary embodiment, a thermogravimeter is assembled as shown inFIGS. 5A and 5B. The solar thermogravimeter 200 comprises a metalpressure vessel 210, a tubular or dome shaped quartz vessel 220 foroptical access, a low vibration vacuum pump 230, an analytical balance240 disposed within the low pressure vessel, a temperature sensor (notshown), a thermocouple (not shown), a flow meter 250 and a gas phasechromatograph or a mass spectrometer 260. An analytical balance 240 isplaced inside a vacuum chamber 245. A sample placed in a sample holder270 is directly irradiated by intense thermal radiation from a high fluxsolar simulator 280. In another embodiment, instead of a solarsimulator, a mirror which reflects solar radiation is used. Thetemperature and pressure conditions closely approach those inside asolar reactor. In an embodiment, the thermogravimeter 200 is a tubular,horizontally illuminated reactor or a dome-shaped, verticallyilluminated reactor. The temperature sensor is a remote temperaturesensor, specifically an IR pyrometer. The IR pyrometer is equipped witha fast shutter that blocks radiation from the solar simulator or mirrorfor short times to minimize IR pyrometer miss-readings due to spillradiation.

The invention is exemplified by the following non-limiting examples.

EXAMPLES Example 1

As shown in FIG. 6, the theoretical data in the graph shows thedisassociation temperature, reaction enthalpy, and losses due to pumpwork as a function of absolute pressure for the iron oxide reactormaterial matrix, specifically, the disassociation temperature as afunction of pressure for the purely thermal reduction reactiontemperature for which the Gibbs free energy change of reaction equalszero. The graph also shows the reaction enthalpy per mole of thereaction and the required pump work for isothermal compression aftercooling to about 300° K per mole of the reaction. In addition, the graphshows that the pump work is one to two orders of magnitude smaller thanthe reaction enthalpy, allowing for low pressure solar reduction.

The output from a thermogravimeter demonstrating the cyclic reactivityfor three redox cycles is shown in FIG. 7. The thermogravimeter measuresthe reaction kinetics for different test materials. The balance measuresthe mass of the reactive material. When the reactive material isreduced, the mass of the sample decreases due to the release of oxygen.When the sample is oxidized, the mass of the sample is increased due tothe addition of oxygen.

Example 2

This example was conducted to demonstrate the manufacturing of themonolithic solid (reactor bed materials 70—referring to the FIGS. 2A and2B) using activated carbon instead of silica. The activated carbon ismixed into ferrite powder and oxidized using either air or steam. Inthis manner, the activated carbon is converted from a solid to a gas,i.e., from carbon to carbon dioxide. Since the activated carbon is allconverted to carbon dioxide during the oxidation, the oxidation of theactivated carbon results in the formation of voids and pores in theferrite material. The resulting porous solid thus contains only theoxidized ferrite powder.

To test this approach, a 0.1 g sample of the activated carbon was testedin a thermogravimeter and oxidized using a flow of 100 cubic centimetersof air during a temperature ramp to 1000° C. at 5° C./min. The resultsof this test are seen in the FIG. 6.

It can be seen above that the onset of oxidation occurs at approximately500° C. and rapid mass loss proceeds. While the FIG. 8 shows that 5%mass remains at the end of the cycle, this is in error due toinstabilities occurring at the beginning of the cycle. This is why thereis also a 5% decrease in weight at the beginning of the test. This isvalidated by the fact that at the end of the test, there was no materialleft in the crucible.

The procedure for making a porous structure (i.e., the monolithic solid)is as follows. Ferrite powder (crushed and sieved to 75 to 125micrometer size) and activated carbon (as received, Fisher Chemical,catalog number C272500) are mixed thoroughly together and placed into aquartz tube reactor. The mixture is then slowly heated (10° C./min)using an inert gas (Nitrogen/Argon) to 1000° C. The mixture is thenreduced using a reducing gas (5% H₂ in Ar) to bring the ferrite powderto its lowest oxidation state. This procedure has no effect on theactivated carbon (already fully reduced). Following this, the powdersare then oxidized using steam at low flow rates at the same temperatureas reduction (1000-1200° C.). This allows for the oxidation of both theferrite powder (Fe to Fe₃O₄, Co to Co₃O₄) and the activated carbon (C toCO₂). However, since the activated carbon becomes a gas and the ferritepowder sinters, the resulting structure after oxidation is a porousmonolithic solid in a ferrite matrix. The voids exist where theactivated carbon once had been. Images of a resulting ACOS structure areshown below in FIG. 9. The resulting porous sintered structure remainsstable after repeated oxidation and reduction cycles at temperatures upto 1500° C. Thus, this structure is very useful for a cyclical loopingprocess that requires thermal reduction at temperatures up to 1400° C.Such a looping process can be used to produce syngas by splitting waterand carbon dioxide using concentrated solar radiation in conjunctionwith the porous metal ferrite structure.

From this example, it may be seen that the activated carbon may beconsumed or converted during the formation of the monolithic solid. Thusthe monolithic solid may comprise a plurality of porous ferriteparticles that are bonded together. In one embodiment, the activatedparticles can be consumed after the formation of the monolithic solid,leaving behind a porous monolithic solid that comprises only a pluralityof ferrite particles that are lightly bonded together.

While the disclosure has been described with reference to exemplaryembodiments, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the disclosure. Inaddition, many modifications may be made to adapt a particular situationor material to the teachings of the disclosure without departing fromthe essential scope thereof. Therefore, it is intended that theinvention not be limited to the particular embodiment disclosed as thebest mode contemplated for carrying out this disclosure.

What is claimed is:
 1. A solar reactor comprising: an outer member; aninner member disposed within an outer member, wherein the outer membersurrounds the inner member and wherein the outer member has an aperturefor receiving solar radiation and wherein an inner cavity and an outercavity are formed by the inner member and the outer member; and areactive material capable of being magnetically stabilized, wherein thereactive material is disposed in the outer cavity between the innermember and the outer member; wherein the reactive material capable ofbeing magnetically stabilized comprises a bed of porous, solidmonolithic material, and wherein the reactive material comprisesactivated carbon and a ferrite prior to being sintered to form the bedof porous, solid monolithic material.
 2. The solar reactor of claim 1,wherein a single inner member is disposed within the outer member. 3.The solar reactor of claim 1, further comprising a shutter disposed uponthe aperture in the outer member, wherein said shutter may be adjustedto an open or a closed position.
 4. The reactor of claim 1, wherein saidouter member further comprises a material port for introducing reactantsmaterials and extracting reaction products.
 5. The solar reactor ofclaim 1, wherein said outer member further comprises a removable frontplate and a removable rear plate which fit over an ends of the innermember and the outer member, respectively.
 6. The solar reactor of claim5, wherein the removable front and the removable rear plate comprisegrooves which align with and fit over the inner member and outer member.7. The solar reactor of claim 6, wherein the inner member, outer member,removable front plate and removable rear plate form a seal whenassembled and placed under a vacuum.
 8. The solar reactor of claim 1,wherein the outer member is at least partially surrounded by insulatingmaterial.
 9. The solar reactor of claim 1, wherein the outer member isat least partially surrounded by a magnetic coil capable of magneticallystabilizing the reactive material.
 10. The solar reactor of claim 1,wherein the solar reactor is used to produce syngas.
 11. A method ofmanufacturing a solar reactor comprising: disposing an inner memberwithin an outer member, wherein the outer member surrounds the innermember and wherein the outer member has an aperture for receiving solarradiation; and disposing a reactive material capable of beingmagnetically stabilized in between the outer member and the innermember; wherein the reactive material capable of being magneticallystabilized comprises a bed of porous, solid monolithic material, andwherein the reactive material comprises activated carbon and a ferriteprior to being sintered to form the bed of porous, solid monolithicmaterial.